type interleaved_format =
  | GL_V2F
  | GL_V3F
  | GL_C4UB_V2F
  | GL_C4UB_V3F
  | GL_C3F_V3F
  | GL_N3F_V3F
  | GL_C4F_N3F_V3F
  | GL_T2F_V3F
  | GL_T4F_V4F
  | GL_T2F_C4UB_V3F
  | GL_T2F_C3F_V3F
  | GL_T2F_N3F_V3F
  | GL_T2F_C4F_N3F_V3F
  | GL_T4F_C4F_N3F_V4F
